This invention relates to a tape reel, particularly to a plastic tape reel which is most suitable for use in video cassettes.
Recently, the demand for video cassette tapes has been rapidly accelerating as a result of the increasing popularity of video recording and reproducing devices. For ease in molding, tape reels widely used for tapes of this type are made exclusively of plastic material. Nevertheless, these tape reels are required to satisfy an extremely rigid fabricative tolerance.
Plastic tape reels having fairly high dimensional accuracy have found popular acceptance. Since the tape reels of this type are destined inevitably by nature to undergo the steps of thermal molding and curing, they tend to sustain sink marks in the process of being cured. Even a slight strain, if allowed to build up in the tape reel, has a strong possibility of producing adverse effects on the quality of images recorded and reproduced with the video devices.
The tape reel of this type generally has a pair of circular flanges axially connected to each other through the medium of an intervening hub. The hub has an outer cylindrical part and an inner cylindrical part disposed concentrically relative to each other, the outer cylindrical part serving as the core upon which the tape is to be wound and the inner cylindrical part permitting the reel engaging shaft of the video device to come into engagement with the interior thereof. Actually for the convenience of fabrication, one of the pair of flanges is integrally molded in advance at one end of the hub and the remaining flange is molded separately. The latter flange is then fastened to the free end of the hub by either ultrasonic welding or snapping engagement.
In the conventional tape reel, the portion for connecting the inner cylindrical part and the outer cylindrical part of the hub to each other in the radial direction has been generally formed by an annular part integrally formed with the flange to be flush therewith. From the standpoint of the flow of molten resin, molding of the integrally formed hub-and-flange inevitably involves two separate paths for the molten resin, the one path extending from the outer edge of the annular part toward the free edge of the outer cylindrical part and the other from the outer edge of the annular part radially toward the circumferential edge of the flange. Thus, a sink mark tends to occur along the line of separation of the paths while the molded resin is being cured. Further, while the outer cylindrical part is being cured, although the basal portion of the outer cylindrical part directly supported by the annular part is allowed to shrink uniformly, the open edge portion of the outer cylindrical part which is intended for eventual engagement with the independently molded flange tends to warp ununiformly inwardly in the radial direction and impair the uniformity of the outside diameter of the outer periphery of the hub on which the tape is to be wound. Such uniformity of outside diameter may lead to such undesirable phenomena as uneven rotation of the hub and uneven winding of the tape and consequently make it necessary to reject the final product.
An object of this invention is to provide a tape reel of a construction such that it can be molded with high dimensional accuracy and ample strength and which is free from the strain resulting from the molding.